New autosomal recessive cerebellar ataxias with oculomotor apraxia

A Review of Ocular Movement Abnormalities in Hereditary Cerebellar Ataxias

Cerebellar ataxias are a wide heterogeneous group of disorders that may present with fine motor deficits as well as gait and balance disturbances that have a significant influence on everyday activities. To review the ocular movements in cerebellar ataxias in order to improve the clinical knowledge of cerebellar ataxias and related subtypes. English papers published from January 1990 to May 2022 were selected by searching PubMed services. The main search keywords were ocular motor, oculomotor, eye movement, eye motility, and ocular motility, along with each ataxia subtype. The eligible papers were analyzed for clinical presentation, involved mutations, the underlying pathology, and ocular movement alterations. Forty-three subtypes of spinocerebellar ataxias and a number of autosomal dominant and autosomal recessive ataxias were discussed in terms of pathology, clinical manifestations, involved mutations, and with a focus on the ocular abnormalities. A flowchart has been made using ocular movement manifestations to differentiate different ataxia subtypes. And underlying pathology of each subtype is reviewed in form of illustrated models to reach a better understanding of each disorder.

Whole-Exome Sequencing Study of Fibroblasts Derived From Patients With Cerebellar Ataxia Referred to Investigate CoQ10 Deficiency

Background and Objectives

Coenzyme Q10(CoQ10)–deficient cerebellar ataxia can be due to pathogenic variants in genes encoding for CoQ10biosynthetic proteins or associated with defects in protein unrelated to its biosynthesis. Diagnosis is crucial because patients may respond favorably to CoQ10supplementation. The aim of this study was to identify through whole-exome sequencing (WES) the pathogenic variants, and assess CoQ10levels, in fibroblasts from patients with undiagnosed cerebellar ataxia referred to investigate CoQ10deficiency.

Methods

WES was performed on genomic DNA extracted from 16 patients. Sequencing data were filtered using a virtual panel of genes associated with CoQ10deficiency and/or cerebellar ataxia. CoQ10levels were measured by high-performance liquid chromatography in 14 patient-derived fibroblasts.

Results

A definite genetic etiology was identified in 8 samples of 16 (diagnostic yield = 50%). The identified genetic causes were pathogenic variants of the genesCOQ8A(ADCK3) (n = 3 samples),ATP1A3(n = 2),PLA2G6(n = 1),SPG7(n = 1), andMFSD8(n = 1). Five novel mutations were found (COQ8An = 3,PLA2G6n = 1, andMFSD8n = 1). CoQ10levels were significantly decreased in 3/14 fibroblast samples (21.4%), 1 carrying compound heterozygousCOQ8Apathogenic variants, 1 harboring a homozygous pathogenicSPG7variant, and 1 with an unknown molecular defect.

Discussion

This work confirms the importance ofCOQ8Agene mutations as a frequent genetic cause of cerebellar ataxia and CoQ10deficiency and suggestsSPG7mutations as a novel cause of secondary CoQ10deficiency.

Ataxia with oculomotor apraxia type 2 caused by a novel homozygous mutation in SETX gene, and literature review

Objectives

Autosomal recessive inherited ataxia with oculomotor apraxia type 2 (AOA2), caused by SETX gene mutations, is characterized by early-onset, progressive cerebellar ataxia, peripheral neuropathy, oculomotor apraxia and elevated serum α-fetoprotein (AFP). This study aimed to expand and summarize the clinical and genetic characteristics of SETX variants related to AOA2.

Methods

The biochemical parameters, electromyogram and radiological findings of the patient were evaluated. Whole-exome sequencing (WES) was performed on the patient using next-generation sequencing (NGS), the variants were confirmed by Sanger sequencing and the pathogenicity of the variants was classified according to the American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines. We reviewed 57 studies of AOA2 patients with SETX mutations and collected clinical and genetic information.

Results

The patient was a 40-year-old Chinese woman who primarily presented with numbness and weakness of the lower limbs in her teenage years. She had elevated AFP, increased serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) and decreased anti-Müllerian hormone (AMH) levels. We identified a novel homozygous missense mutation of the SETX gene, c.7118 C>T (p. Thr2373Ile), in the patient via Whole-exome and Sanger sequencing. The variant was located in the DNA/RNA helicase domain and is highly conserved. The protein prediction analysis verified the SETX variant as a damaging alteration and ACMG/AMP guidelines classified it as likely pathogenic. Through a literature review, we identified 229 AOA2 cases with SETX variants, and among the variants, 156 SETX variants were exonic. We found that 107 (46.7%) patients were European, 50 (21.8%) were African and 48 (21.0%) were Asian. Among the Asian patients, five from two families were Mainland Chinese. The main clinical features were cerebellar ataxia (100%), peripheral neuropathy (94.6%), cerebellar atrophy (95.3%) and elevated AFP concentration (92.0%). Most reported SETX mutations in AOA2 patients were missense, frameshift and nonsense mutations.

Conclusion

We discovered a novel homozygous variant of the SETX gene as a cause of AOA2 in the current patient and expanded the genotypic spectrum of AOA2. Moreover, the clinical features of AOA2 and genetic findings in SETX were assessed in reported cohorts and are summarized in the present study.

Inherited Cerebellar Ataxias: 5-Year Experience of the Irish National Ataxia Clinic

Establishing a molecular diagnosis in patients with progressive ataxia is often challenging due to significant genetic and clinical heterogeneity and requires a methodical approach with expert clinical evaluation and investigations. We describe the 5-year experience of the National Ataxia Clinic (NAC), Ireland. All adults with ataxia attending the NAC between 2014 and 2019 were evaluated. All individuals underwent detailed clinical assessment and investigations including, where appropriate, genetic testing using next-generation sequencing. For all patients, acquired causes were ruled out. A total of 254 patients from 196 families were assessed; with growth of the clinic cohort by 82% from 133 to 242 over the 5-year period. The underlying genetic cause was identified in 128/196 probands (65.3%). The detection rate for repeat expansion disorder gene testing was 47.7% (82/172) and using NGS gene panel, a genetic diagnosis was obtained in 30/84 (35.7%). Whole exome sequencing identified the molecular diagnosis in 4/20 (20%), and whole genome sequencing provided genetic diagnosis in 1/5 (20%). The commonest diagnosis was Friedreich's ataxia (68/128, 53.1%). SPG7-associated ataxia was the second most common diagnosis (21/128, 16.4%), followed by ANO10-associated spastic ataxia, ataxia telangiectasia (AT), and other rarer phenotypes. Our results highlight that careful clinical phenotyping in a dedicated ataxia clinic is crucial for appropriate genetic testing in selected patients in a timely manner. Advanced genetic testing has significantly improved the diagnostic yield in patients with suspected genetic ataxia and should be considered in all individuals with negative repeat expansion testing.

Transcription-associated events affecting genomic integrity

Accurate maintenance of genomic as well as epigenomic integrity is critical for proper cell and organ function. Continuous exposure to DNA damage is, thus, often associated with malignant transformation and degenerative diseases. A significant, chronic threat to genome integrity lies in the process of transcription, which can result in the formation of potentially harmful RNA : DNA hybrid structures (R-loops) and has been linked to DNA damage accumulation as well as dynamic chromatin reorganization. In sharp contrast, recent evidence suggests that active transcription, the resulting transcripts as well as R-loop formation can play multi-faceted roles in maintaining and restoring genome integrity. Here, we will discuss the emerging contributions of transcription as both a source of DNA damage and a mediator of DNA repair. We propose that both aspects have significant implications for genome maintenance, and will speculate on possible long-term consequences for the epigenetic integrity of transcribing cells.This article is part of the themed issue 'Chromatin modifiers and remodellers in DNA repair and signalling'.

Increased oxidative stress in AOA3 cells disturbs ATM-dependent DNA damage responses

Ataxia telangiectasia (AT) is caused by a mutation in the ataxia-telangiectasia-mutated (ATM) gene; the condition is associated with hyper-radiosensitivity, abnormal cell-cycle checkpoints, and genomic instability. AT patients also show cerebellar ataxia, possibly due to reactive oxygen species (ROS) sensitivity in neural cells. The ATM protein is a key regulator of the DNA damage response. Recently, several AT-like disorders have been reported. The genes responsible for them are predicted to encode proteins that interact with ATM in the DNA-damage response. Ataxia with oculomotor apraxia types 1-3 (AOA1, 2, and 3) result in a neurodegenerative and cellular phenotype similar to AT; however, the basis of this phenotypic similarity is unclear. Here, we show that the cells of AOA3 patients display aberrant ATM-dependent phosphorylation and apoptosis following γ-irradiation. The ATM-dependent response to H2O2 treatment was abrogated in AOA3 cells. Furthermore, AOA3 cells had reduced ATM activity. Our results suggest that the attenuated ATM-related response is caused by an increase in endogenous ROS in AOA3 cells. Pretreatment of cells with pyocyanin, which induces endogenous ROS production, abolished the ATM-dependent response. Moreover, AOA3 cells had decreased homologous recombination (HR) activity, and pyocyanin pretreatment reduced HR activity in HeLa cells. These results indicate that excess endogenous ROS represses the ATM-dependent cellular response and HR repair in AOA3 cells. Since the ATM-dependent cell-cycle checkpoint is an important block to carcinogenesis, such inactivation of ATM may lead to tumorigenesis as well as neurodegeneration.

Ataxias with Autosomal, X-Chromosomal or Maternal Inheritance

Heredoataxias are a group of genetic disorders with a cerebellar syndrome as the leading clinical manifestation. The current classification distinguishes heredoataxias according to the trait of inheritance into autosomal dominant, autosomal recessive, X-linked, and maternally inherited heredoataxias. The autosomal dominant heredoataxias are separated into spinocerebellar ataxias (SCA1-8, 10-15, 17-23, 25-30, and dentato-rubro-pallido-luysian atrophy), episodic ataxias (EA1-7), and autosomal dominant mitochondrial heredoataxias (Leigh syndrome, MIRAS, ADOAD, and AD-CPEO). The autosomal recessive ataxias are separated into Friedreich ataxia, ataxia due to vitamin E deficiency, ataxia due to Abeta-lipoproteinemia, Refsum disease, late-onset Tay-Sachs disease, cerebrotendineous xanthomatosis, spinocerebellar ataxia with axonal neuropathy, ataxia telangiectasia, ataxia telangiectasia-like disorder, ataxia with oculomotor apraxia 1 and 2, spastic ataxia of Charlevoix-Saguenay, Cayman ataxia, Marinesco-Sjögren syndrome, and autosomal recessive mitochondrial ataxias (AR-CPEO, SANDO, SCAE, AHS, IOSCA, MEMSA, LBSL CoQ-deficiency, PDC-deficiency). Only two of the heredoataxias, fragile X/tremor/ataxia syndrome, and XLSA/A are transmitted via an X-linked trait. Maternally inherited heredoataxias are due to point mutations in genes encoding for tRNAs, rRNAs, respiratory chain subunits or single large scale deletions/duplications of the mitochondrial DNA and include MELAS, MERRF, KSS, PS, MILS, NARP, and non-syndromic mitochondrial disorders. Treatment of heredoataxias is symptomatic and supportive and may have a beneficial effect in single patients.

**Please see page 424 for abbreviation list.

Novel SETX variants in a patient with ataxia, neuropathy, and oculomotor apraxia are associated with normal sensitivity to oxidative DNA damaging agents

BACKGROUND

Homozygous and compound heterozygous mutations in SETX are associated with AOA2 disease, a recessive form of ataxia with oculomotor apraxia and neuropathy with onset of ataxia between the first and second decade of life. The majority of the AOA2 mutated cell lines tested show hypersensitivity to oxidative DNA damaging agents, with one exception.

RESULTS

We describe a patient presenting with early-onset progressive ataxia, oculomotor apraxia, axonal sensory-motor neuropathy, optic atrophy, delayed psychomotor development, and a behavior disorder. The patient carries two novel missense variants in the SETX gene. Based on the hypothesis that the patient's clinical phenotype may represent an atypical form of the AOA2 disease, we tested the patient-derived cell line for hypersensitivity to oxidative DNA damaging agents, with negative results.

CONCLUSIONS

The lack of hypersensitivity we observed may be explained either by considering the atypical clinical picture of the patient analyzed or, alternatively, by hypothesizing that the variants detected are not the cause of the observed phenotype. Consistent with the first hypothesis of an atypical AOA2 form and based on the multiple functions of senataxin reported so far, it is likely that different sets of SETX mutations/variants may have variable functional effects that still need to be functionally characterized. The possibility that the severe and complicated clinical picture presented by the patient described here represents a clinical entity differing from the known recessive ataxias should be considered as well.

Ataxia with oculomotor apraxia type 2 fibroblasts exhibit increased susceptibility to oxidative DNA damage

Ataxia with oculomotor apraxia type 2 (AOA2) is an autosomal recessive cerebellar ataxia associated with mutations in SETX, which encodes the senataxin protein, a DNA/RNA helicase. We describe the clinical phenotype and molecular characterization of a Colombian AOA2 patient who is compound heterozygous for a c.994 C>T (p.R332W) missense mutation in exon 7 and a c.6848_6851delCAGA (p.T2283KfsX32) frameshift deletion in SETX exon 21. Immunocytochemistry of patient-derived fibroblasts revealed a normal cellular distribution of the senataxin protein, suggesting that these mutations do not lead to loss or mis-localization of the protein, but rather that aberrant function of senataxin underlies the disease pathogenesis. Furthermore, we used the alkaline comet assay to demonstrate that patient-derived fibroblast cells exhibit an increased susceptibility to oxidative DNA damage. This assay provides a novel and additional means to establish pathogenicity of SETX mutations.

The global epidemiology of hereditary ataxia and spastic paraplegia: a systematic review of prevalence studies

BACKGROUND

Hereditary cerebellar ataxias (HCA) and hereditary spastic paraplegias (HSP) are two groups of neurodegenerative disorders that usually present with progressive gait impairment, often leading to permanent disability. Advances in genetic research in the last decades have improved their diagnosis and brought new possibilities for prevention and future treatments. Still, there is great uncertainty regarding their global epidemiology.

SUMMARY

Our objective was to assess the global distribution and prevalence of HCA and HSP by a systematic review and meta-analysis of prevalence studies. The MEDLINE, ISI Web of Science and Scopus databases were searched (1983-2013) for studies performed in well-defined populations and geographical regions. Two independent reviewers assessed the studies and extracted data and predefined methodological parameters. Overall, 22 studies were included, reporting on 14,539 patients from 16 countries. Multisource population-based studies yielded higher prevalence values than studies based primarily on hospitals or genetic centres. The prevalence range of dominant HCA was 0.0-5.6/10(5), with an average of 2.7/10(5) (1.5-4.0/10(5)). Spinocerebellar ataxia type 3 (SCA3)/Machado-Joseph disease was the most common dominant ataxia, followed by SCA2 and SCA6. The autosomal recessive (AR) HCA (AR-HCA) prevalence range was 0.0-7.2/10(5), the average being 3.3/10(5) (1.8-4.9/10(5)). Friedreich ataxia was the most frequent AR-HCA, followed by ataxia with oculomotor apraxia or ataxia-telangiectasia. The prevalence of autosomal dominant (AD) HSP (AD-HSP) ranged from 0.5 to 5.5/10(5) and that of AR-HSP from 0.0 to 5.3/10(5), with pooled averages of 1.8/10(5) (95% CI: 1.0-2.7/10(5)) and 1.8/10(5) (95% CI: 1.0-2.6/10(5)), respectively. The most common AD-HSP form in every population was spastic paraplegia, autosomal dominant, type 4 (SPG4), followed by SPG3A, while SPG11 was the most frequent AR-HSP, followed by SPG15. In population-based studies, the number of families without genetic diagnosis after systematic testing ranged from 33 to 92% in the AD-HCA group, and was 40-46% in the AR-HCA, 45-67% in the AD-HSP and 71-82% in the AR-HSP groups.

KEY MESSAGES

Highly variable prevalence values for HCA and HSP are reported across the world. This variation reflects the different genetic make-up of the populations, but also methodological heterogeneity. Large areas of the world remain without prevalence studies. From the available data, we estimated that around 1:10,000 people are affected by HCA or HSP. In spite of advances in genetic research, most families in population-based series remain without identified genetic mutation after extensive testing. © 2014 S. Karger AG, Basel.

Mitochondrial dysfunction in a novel form of autosomal recessive ataxia

Defects in the recognition and/or repair of damage to DNA are responsible for a sub-group of autosomal recessive ataxias. Included in this group is a novel form of ataxia with oculomotor apraxia characterised by sensitivity to DNA damaging agents, a defect in p53 stabilisation, oxidative stress and resistance to apoptosis. We provide evidence here that the defect in this patient's cells is at the level of the mitochondrion. Mitochondrial membrane potential was markedly reduced in cells from the patient and ROS levels were elevated. This was accompanied by lipid peroxidation of mitochondrial proteins involved in electron transport and RNA synthesis. However, no gross changes or alteration in composition or activity of mitochondrial electron transport complexes was evident. Sequencing of mitochondrial DNA revealed a mutation, I349T, in the mitochondrial cytochrome b gene. These results describe a patient with an apparently novel form of AOA characterised by a defect at the level of the mitochondrion.

Ataxia with oculomotor apraxia type1 (AOA1): novel and recurrent aprataxin mutations, coenzyme Q10 analyses, and clinical findings in Italian patients

Ataxia with oculomotor apraxia type1 (AOA1, MIM 208920) is a rare autosomal recessive disease caused by mutations in the APTX gene. We screened a cohort of 204 patients with cerebellar ataxia and 52 patients with early-onset isolated chorea. APTX gene mutations were found in 13 ataxic patients (6%). Eleven patients were homozygous for the known p.W279X, p.W279R, and p.P206L mutations. Three novel APTX mutations were identified: c.477delC (p.I159fsX171), c.C541T (p.Q181X), and c.C916T (p.R306X). Expression of mutated proteins in lymphocytes from these patients was greatly decreased. No mutations were identified in subjects with isolated chorea. Two heterozygous APTX sequence variants (p.L248M and p.D185E) were found in six families with ataxic phenotype. Analyses of coenzyme Q10 in muscle, fibroblasts, and plasma demonstrated normal levels of coenzyme in five of six mutated subjects. The clinical phenotype was homogeneous, irrespectively of the type and location of the APTX mutation, and it was mainly characterized by early-onset cerebellar signs, sensory neuropathy, cognitive decline, and oculomotor deficits. Three cases had slightly raised alpha-fetoprotein. Our survey describes one of the largest series of AOA1 patients and contributes in defining clinical, molecular, and biochemical characteristics of this rare hereditary neurological condition.

(1)H MR spectroscopy in Friedreich's ataxia and ataxia with oculomotor apraxia type 2

BACKGROUND AND AIM

Friedreich's ataxia (FRDA) and ataxia with oculomotor apraxia type 2 (AOA2) are the two most frequent forms of autosomal recessive cerebellar ataxias. However, brain metabolism in these disorders is poorly characterized and biomarkers of the disease progression are lacking. We aimed at assessing the neurochemical profile of the pons, the cerebellar hemisphere and the vermis in patients with FRDA and AOA2 to identify potential biomarkers of these diseases.

METHODS

Short-echo, single-voxel proton ((1)H) magnetic resonance spectroscopy data were acquired from 8 volunteers with FRDA, 9 volunteers with AOA2, and 38 control volunteers at 4T. Disease severity was assessed by the Friedreich's Ataxia Rating Scale (FARS).

RESULTS

Neuronal loss/dysfunction was indicated in the cerebellar vermis and hemispheres in both diseases by lower total N-acetylaspartate levels than controls. The putative gliosis marker myo-inositol was higher than controls in the vermis and pons in AOA2 and in the vermis in FRDA. Total creatine, another potential gliosis marker, was higher in the cerebellar hemispheres in FRDA relative to controls. Higher glutamine in FRDA and lower glutamate in AOA2 than controls were observed in the vermis, indicating different mechanisms possibly leading to altered glutamatergic neurotransmission. In AOA2, total N-acetylaspartate levels in the cerebellum strongly correlated with the FARS score (p<0.01).

CONCLUSION

Distinct neurochemical patterns were observed in the two patient populations, warranting further studies with larger patient populations to determine if the alterations in metabolite levels observed here may be utilized to monitor disease progression and treatment.

EFNS guidelines on the molecular diagnosis of ataxias and spastic paraplegias

BACKGROUND AND PURPOSE

These EFNS guidelines on the molecular diagnosis of neurogenetic disorders are designed to provide practical help for the general neurologist to make appropriate use of molecular genetics in diagnosing neurogenetic disorders.

METHODS

Literature searches were performed before expert members of the task force wrote proposals, which were discussed in detail until final consensus had been reached among all task force members.

RESULTS AND CONCLUSION

This paper provides updated guidelines for molecular diagnosis of two particularly complex groups of disorders, the ataxias and spastic paraplegias. Possibilities and limitations of molecular genetic diagnosis of these disorders are evaluated and recommendations are provided.

Ataxia with oculomotor apraxia type 2: clinical, biological and genotype/phenotype correlation study of a cohort of 90 patients

Ataxia with oculomotor apraxia type 2 (AOA2) is an autosomal recessive disease due to mutations in the senataxin gene, causing progressive cerebellar ataxia with peripheral neuropathy, cerebellar atrophy, occasional oculomotor apraxia and elevated alpha-feto-protein (AFP) serum level. We compiled a series of 67 previously reported and 58 novel ataxic patients who underwent senataxin gene sequencing because of suspected AOA2. An AOA2 diagnosis was established for 90 patients, originating from 15 countries worldwide, and 25 new senataxin gene mutations were found. In patients with AOA2, median AFP serum level was 31.0 microg/l at diagnosis, which was higher than the median AFP level of AOA2 negative patients: 13.8 microg/l, P = 0.0004; itself higher than the normal level (3.4 microg/l, range from 0.5 to 17.2 microg/l) because elevated AFP was one of the possible selection criteria. Polyneuropathy was found in 97.5% of AOA2 patients, cerebellar atrophy in 96%, occasional oculomotor apraxia in 51%, pyramidal signs in 20.5%, head tremor in 14%, dystonia in 13.5%, strabismus in 12.3% and chorea in 9.5%. No patient was lacking both peripheral neuropathy and cerebellar atrophy. The age at onset and presence of occasional oculomotor apraxia were negatively correlated to the progression rate of the disease (P = 0.03 and P = 0.009, respectively), whereas strabismus was positively correlated to the progression rate (P = 0.03). An increased AFP level as well as cerebellar atrophy seem to be stable in the course of the disease and to occur mostly at or before the onset of the disease. One of the two patients with a normal AFP level at diagnosis had high AFP levels 4 years later, while the other had borderline levels. The probability of missing AOA2 diagnosis, in case of sequencing senataxin gene only in non-Friedreich ataxia non-ataxia-telangiectasia ataxic patients with AFP level > or =7 microg/l, is 0.23% and the probability for a non-Friedreich ataxia non-ataxia-telangiectasia ataxic patient to be affected with AOA2 with AFP levels > or =7 microg/l is 46%. Therefore, selection of patients with an AFP level above 7 microg/l for senataxin gene sequencing is a good strategy for AOA2 diagnosis. Pyramidal signs and dystonia were more frequent and disease was less severe with missense mutations in the helicase domain of senataxin gene than with missense mutations out of helicase domain and deletion and nonsense mutations (P = 0.001, P = 0.008 and P = 0.01, respectively). The lack of pyramidal signs in most patients may be explained by masking due to severe motor neuropathy.

Functional role for senataxin, defective in ataxia oculomotor apraxia type 2, in transcriptional regulation

Ataxia oculomotor apraxia type 2 (AOA2) is an autosomal recessive neurodegenerative disorder characterized by cerebellar ataxia and oculomotor apraxia. The gene mutated in AOA2, SETX, encodes senataxin, a putative DNA/RNA helicase which shares high homology to the yeast Sen1p protein and has been shown to play a role in the response to oxidative stress. To investigate further the function of senataxin, we identified novel senataxin-interacting proteins, the majority of which are involved in transcription and RNA processing, including RNA polymerase II. Binding of RNA polymerase II to candidate genes was significantly reduced in senataxin deficient cells and this was accompanied by decreased transcription of these genes, suggesting a role for senataxin in the regulation/modulation of transcription. RNA polymerase II-dependent transcription termination was defective in cells depleted of senataxin in keeping with the observed interaction of senataxin with poly(A) binding proteins 1 and 2. Splicing efficiency of specific mRNAs and alternate splice-site selection of both endogenous genes and artificial minigenes were altered in senataxin depleted cells. These data suggest that senataxin, similar to its yeast homolog Sen1p, plays a role in coordinating transcriptional events, in addition to its role in DNA repair.

[Autosomal recessive cerebellar ataxias]

Friedreich ataxia is the most frequent recessive cerebral ataxia d should always be researched first. Ataxia with isolated vitamin E deficiency and abetalipoproteinemia have a specific treatment. Associated neurological signs such polyneuroapthy, ophtalmologic or oculomotor signs, pyramidal signs, and cerebellar MRI can lead to the etiological diagnosis. Biological tests should be: vitamin E, cholesterol, alpha-fetoprotein levels, acanthocytes, than phytanic acid, cholestanol, lysosomal enzymes. Numerous autosomal recessive cerebellar ataxia remain without etiology.

Epidemiological, clinical, paraclinical and molecular study of a cohort of 102 patients affected with autosomal recessive progressive cerebellar ataxia from Alsace, Eastern France: implications for clinical management

While Friedreich's ataxia (FRDA) and ataxia telangiectasia (AT) are known to be the two most frequent forms of autosomal recessive cerebellar ataxia (ARCA), knowledge on the other forms of ARCA has been obtained only recently, and they appear to be rarer. Little is known about the epidemiological features and the relative frequency of the ARCAs and only few data are available about the comparative features of ARCAs. We prospectively studied 102 suspected ARCA cases from Eastern France (including 95 from the Alsace region) between 2002 and 2008. The diagnostic procedure was based on a sequential strategic scheme. We examined the clinical, paraclinical and molecular features of the large cohort of patients and compared features and epidemiology according to molecular diagnosis. A molecular diagnosis could be established for 57 patients; 36 were affected with FRDA, seven with ataxia plus oculomotor apraxia type 2 (AOA2), four with AT, three with ataxia plus oculomotor apraxia type 1 (AOA1), three with Marinesco-Sjögren syndrome, two with autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS), one with ataxia with vitamin E deficiency (AVED) and one with autosomal recessive cerebellar ataxia type 2 (ARCA2). The group of patients with no identified mutation had a significantly lower spinocerebellar degeneration functional score corrected for disease duration (SDFS/DD ratio; p = 0.002) and comprised a significantly higher proportion of cases with onset after 20 years (p < 0.01). Extensor plantar reflexes were rarer and cerebellar atrophy was more frequent in the group of patients with a known non-Friedreich ARCA compared to all other patients (p < 0.0001 and p = 0.0003, respectively). Lower limb areflexia and electroneuromyographic evidences of peripheral neuropathy were more frequent in the Friedreich ataxia group than in the group with a known non-Friedreich ataxia and were more frequent in the later group than in the group with no identified mutation (p = 0.0001 and p = 0.01, respectively). The overall prevalence of ARCA in Alsace is 1/19,000. We can infer the prevalence of FRDA in Alsace to be 1/50,000 and infer that AT is approximately eight times less frequent than FRDA. MSS, AOA2 and ARSACS appear only slightly less frequent than AT. Despite the broad variability of severity, Friedreich ataxia patients are clinically distinct from the other forms of ARCA. Patients with no identified mutation have more often a pure cerebellar degenerative disease or a spastic ataxia phenotype. It appears that ARCA cases can be divided into two major groups of different prognosis, an early-onset group with a highly probable genetic cause and an adult-onset group with better prognosis for which a genetic cause is more difficult to prove but not excluded. ARCAs are rare, early-disabling and genetically heterogeneous diseases dominated by FRDA. Several of the recently identified ARCAs, such as AVED, ARSACS, AOA1, AOA2 and MSS, have a prevalence close to AT and should be searched for extensively irrespective of ethnic origins. The strategic scheme is a useful tool for the diagnosis of ARCAs in clinical practice.

A rapid flow cytometry test based on histone H2AX phosphorylation for the sensitive and specific diagnosis of ataxia telangiectasia

Ataxia telangiectasia (A-T) is a progressive neurodegenerative disease with onset in early childhood, caused by mutations in the ATM (ataxia-telangiectasia mutated) gene. Diagnosis relies on laboratory tests showing high levels of serum alphafetoprotein, cell sensitivity to ionizing radiation (IR) and absence or reduced levels of ATM protein. Many tests, however, are not sufficiently sensitive or specific for A-T, have long turnaround times, or require large blood samples. This prompted us to develop a new flow cytometry method for the diagnosis of A-T based on the measurement of histone H2AX phosphorylation. We established normal ranges of histone H2AX phosphorylation after 2 Gy IR by testing T-cell lines, lymphoblastoid cell lines (LCLs) and/or peripheral blood mononuclear cells (PBMCs) or both from 20 genetically proven A-T and 46 control donors. To further evaluate the specificity and sensitivity of the test, we analyzed cells from 19 patients suspected of having A-T, and from one Friedreich Ataxia, one Ataxia with Oculomotor Apraxia type 2, and one Nijmegen Breakage Syndrome patients. Phosphorylated histone H2AX mean fluorescence intensity of irradiated A-T cells was significantly lower than that of healthy donors. The intrastaining, intraassay, and interassay imprecisions were <or=13.22%. Sensitivity and specificity were virtually 100% when the test was performed on PBMCs. Screening of 19 consecutive new patients with suspected A-T classified 15 patients as non-A-T and four as A-T; diagnosis of the latter four was subsequently confirmed by DNA sequencing to identify ATM mutations. The Friedreich Ataxia patient, the Ataxia with Oculomotor Apraxia type 2 patient and the Nijmegen Breakage Syndrome patient were classified as non-A-T. This flow cytometry test is very sensitive, specific and rapid, and requires only 2 ml of blood. It may thus be proposed for the early differential diagnosis of A-T as an alternative to methods requiring the production of LCLs.

Senataxin, defective in ataxia oculomotor apraxia type 2, is involved in the defense against oxidative DNA damage

Adefective response to DNA damage is observed in several human autosomal recessive ataxias with oculomotor apraxia, including ataxia-telangiectasia. We report that senataxin, defective in ataxia oculomotor apraxia (AOA) type 2, is a nuclear protein involved in the DNA damage response. AOA2 cells are sensitive to H₂O₂, camptothecin, and mitomycin C, but not to ionizing radiation, and sensitivity was rescued with full-length SETX cDNA. AOA2 cells exhibited constitutive oxidative DNA damage and enhanced chromosomal instability in response to H₂O₂. Rejoining of H₂O₂-induced DNA double-strand breaks (DSBs) was significantly reduced in AOA2 cells compared to controls, and there was no evidence for a defect in DNA single-strand break repair. This defect in DSB repair was corrected by full-length SETX cDNA. These results provide evidence that an additional member of the autosomal recessive AOA is also characterized by a defective response to DNA damage, which may contribute to the neurodegeneration seen in this syndrome.

Seminar on choreas

Chorea is one of the major types of involuntary movement disorders originating from dysfunctional neuronal networks interconnecting the basal ganglia and frontal cortical motor areas. The syndrome is characterised by a continuous flow of random, brief, involuntary muscle contractions and can result from a wide variety of causes. Diagnostic work-up can be straightforward in patients with a positive family history of Huntington's disease or acute-onset hemichorea in patients with lacunar stroke, but it can be a challenging and complex task in rare autoimmune or genetic choreas. Principles of management focus on establishing an aetiological classification and, if possible, removal of the cause. Preventive strategies may be possible in Huntington's disease where genetic counselling plays a major part. In this review we summarise the current understanding of the neuroanatomy and pathophysiology of chorea, its major aetiological classes, and principles of diagnostic work-up and management.

The molecular genetics of non-ALS motor neuron diseases

Hereditary disorders of voluntary motor neurons are individually relatively uncommon, but have the potential to provide significant insights into motor neuron function in general and into the mechanisms underlying the more common form of sporadic Amyotrophic Lateral Sclerosis. Recently, mutations in a number of novel genes have been associated with Lower Motor Neuron (HSPB1, HSPB8, GARS, Dynactin), Upper Motor Neuron (Spastin, Atlastin, Paraplegin, HSP60, KIF5A, NIPA1) or mixed ALS-like phenotypes (Alsin, Senataxin, VAPB, BSCL2). In comparison to sporadic ALS these conditions are usually associated with slow progression, but as experience increases, a wide variation in clinical phenotype has become apparent. At the molecular level common themes are emerging that point to areas of specific vulnerability for motor neurons such as axonal transport, endosomal trafficking and RNA processing. We review the clinical and molecular features of this diverse group of genetically determined conditions and consider the implications for the broad group of motor neuron diseases in general.